The present invention relates to a hammer bank rocking device in an impact dot line printer equipped with a plurality of printing heads along printing lines.
FIG. 1 shows a structure of a conventional linear motor type impact dot line printer. Reference numeral 1 designates a hammer bank equipped with a plurality of printing heads along printing lines; 3 a hammer bank mounting bed provided with repelling portions 3a and 3b; and 9 a coil core plate and counter balancer provided with repelling portions 9a and 9b and equipped with coils 8 and 8'.
The counter balancer 9 is provided in parallel with the hammer bank mounting bed 3 and connected to upper and lower portions of a belt 5 extended between rotational drums 4 and 4' provided on opposite sides thereof so that the counter balancer 9 and the hammer bank 1 are rocked in a direction reverse to each other.
The coils 8 and 8' face permanent magnets 6 and 6', respectively, of a magnetic circuit comprising permanent magnets 6 and 6' and a yoke 7 secured to a frame (not shown). When a reverse current is supplied to the coils 8 and 8' at regular intervals, the counter balancer 9 and the hammer bank 1 are rocked in the directions reverse to each other.
Reference numerals 10-1, 10-2, 10-3 and 10-4 designate repelling springs provided on opposite sides in order to reduce the thrust required for deceleration at the end of the rocking stroke of the hammer bank 1 and the counter bank 9. Reference numeral 11 designates an ink ribbon; 12 a printing paper; and 13 a platen.
In the conventional hammer bank rocking device shown in FIG. 1, the hammer bank mounting bed 3 and the counter balancer 9 simultaneously collide with the left and right repelling springs opposed to each other at the end of the shuttling operation. However, in the conventional construction shown in FIG. 1, a couple F.sub.1 .times.2l.sub.1 is produced which is expressed by product of a force F.sub.1 caused by the collision and a length 2l.sub.1 between axes of the hammer bank mounting bed 3 and the counter balancer 9, and as a result, a shock force by which the hammer bank mounting bed 3 is rotated acts, resulting in vibrations and noises that give rise to the lowering of printing-dot precision.